Gearset, in particular for electric hand machine tools

ABSTRACT

A gear mechanism, in particular for hand power tools, is disclosed which has a driving gear wheel ( 12 ), seated on a drive shaft ( 11 ) in the manner fixed against relative rotation, and a driven gear wheel ( 13 ), meshing with the driving gear wheel and driving a driven shaft ( 14 ). To attain high running smoothness of the gear mechanism and a longer service life by reducing the mechanical load on the gearing upon startup and in load peaks that occur during operation, spring-elastic damping elements ( 22 ) are located between the driven gear wheel ( 13 ) and the driven shaft ( 14 ) (FIG.  2 ).

PRIOR ART

The invention is based on a gear mechanism, in particular for hand powertools, as generically defined by the preamble to claim 1.

In gear mechanisms for hand power tools, sintered gear wheels with aspiral or straight gearing are used, for reasons of cost. Recourse togear wheels that are cut, whose production costs are relatively high, ishad only whenever stringent demands for running smoothness are made, inthe case of high-quality appliances. Plastic gear wheels, which can beproduced at a similar cost to sintered gear wheels, can transmit onlylow torques and are therefore used in hand power tools only in a fewexceptional cases.

Pairs of gear wheels put together from sintered gear wheels have thedisadvantage, dictated by their production, of major tolerances, whichcauses loud running noise and has an adverse effect on the service life.

ADVANTAGES OF THE INVENTION

The gear mechanism of the invention, in particular for hand power tools,having the characteristics of claim 1 has the advantage that because ofthe damping elements incorporated between the damping elements,preferably of rubber or rubberlike material with a high damping factor,that are incorporated between the driving gear wheel and the drivenshaft and act in the circumferential direction or tangential direction,tolerances and in particular pitch errors, profile deviation and errorsof concentricity, existing in the paired gear wheels can not only becompensated for, markedly lessening the gear noise and vibration causedby the gear mechanism, but the very high startup forces acting on thegearing, which occur when the drive motor that turns the drive shaftupon being switched on because of the inertia of the drive and of thedriven masses, and the load peaks that occur in operation at the gearingcan all be reduced. Overall, this leads to highly smooth running in thecase of sintered gear wheels, and regardless of the type of gear wheels(sintered or cut), because of the reduced mechanical load, the result isa long service life of the gear mechanism.

By the provisions recited in the further claims, advantageousrefinements of and improvements to the gear mechanism defined by claim 1are possible.

In a preferred embodiment of the invention, the driven gear wheel isseated rotatably on the driven shaft and has pockets, offset from oneanother in the circumferential direction, that are defined by radialside walls. The damping elements rest in the pockets with contactagainst the radial side walls and are retained on a slaving device thatis joined to the driven shaft in a manner fixed against relativerotation, which slaving device is fixed axially nondisplaceably on thedriven shaft.

In an advantageous embodiment of the invention, the slaving device has aring seated on the driven shaft in force- and form-locking fashion andhas a number of radial ribs, corresponding to the number of pockets inthe driven gear wheel, of which each radial rib protrudes into onepocket. In each pocket, there are two damping elements, resting on eachside of the radial rib, of which each damping element is braced on oneside on the radial rib and on the other on a radial side wall of thepocket. The damping elements may be placed in the pockets or joined tothe radial ribs, for instance spray-coated onto the radial ribs.

DRAWING

The invention is described in further detail in the ensuing descriptionin terms of an exemplary embodiment shown in the drawing. Shown are:

FIG. 1, an exploded of an angular gear for a hand power tool;

FIG. 2, a perspective view of the assembled gear mechanism in FIG. 1;

FIG. 3, a matrix for clear comparison of possible pocket and radial ribgeometries in the gear mechanism of FIGS. 1 and 2.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

The angular gear, sketched in an exploded view in FIG. 1, for a handpower tool as an exemplary embodiment for a gear mechanism in generalhas a drive shaft 11, which can be driven by an electric motor; adriving gear wheel 12, seated in a manner fixed against relativerotation on the drive shaft 11 and embodied here as a conical pinionwith pinion gearing 121; a driven gear wheel 13 meshing with the drivinggear wheel 12, which driven gear wheel is embodied as a ring gear withspur gearing 131; and a driven shaft 14, driven by the driven gear wheel13. The driven gear wheel 13 sits without play, rotatably and axiallynondisplaceably, on the driven shaft 14; in the axial direction, it isbraced on one side on an annular shoulder 15 (FIG. 1) embodied on thedriven shaft 14 and on the other on a slaving device 16, which ispressed onto the driven shaft 14 and is additionally joined byforce-locking to the driven shaft 14. The slaving device 16 has both aring 17, surrounding the driven shaft 14, and a plurality of radial ribs18, in this exemplary embodiment three of them, that are offset in thecircumferential direction and are embodied integrally with the ring 17or instead are in multiple parts. The driven shaft 14, in the region ofthe ring 17, has two diametrically located axial grooves 19, and thering 17 has two diametrically located cams 20, protruding from the innersurface of the ring, which plunge in form-locking fashion into the axialgrooves 19. In the exemplary embodiment, the radial ribs 18 are offsetby equal circumferential angles and each protrude centrally into pockets21 that are integrally formed in the driven gear wheel 13 at the samerotational angle spacing as the radial ribs 18. The pockets 21 are eachdefined in the circumferential direction by radially oriented side walls211. Two damping elements 22 of spring-elastic material, such as rubber,are located in each pocket 21, and each damping element 22 rests on oneside on a radial rib 18 and on the other on a side wall 211 of thepocket 21. The damping elements 22 are either inserted into the pockets21 upon the assembly of the gear mechanism, or are solidly joinedbeforehand to the radial ribs 18.

When the electric motor is switched on, the torque is transmitted fromthe drive shaft 11 to the driven gear wheel 13 via the driving gearwheel 12. Since the driven gear wheel 13 is seated rotatably on thedriven shaft 14, the driven gear wheel 13 can initially rotate by a fewdegrees, compressing the damping element 22 located behind it in thedirection of rotation, and then, via the radial ribs 18, it can rotatethe slaving device 16 and—since the slaving device 16 is seated on thedriven shaft 14 in a manner fixed against relative rotation—it can drivethe driven shaft 14. Thus by means of the damping elements 22, rotationis made to occurs in the driven gear wheel 13 even without rotationoccurring at the driven shaft 14. As a result of this delay, the maximumacceleration that occurs is reduced, and the time until the full idlingrpm of the driven shaft 14 is reached is prolonged. Thus the heavy loadon the gearing between the driving gear wheel 12 and the driven gearwheel 13 upon startup is reduced.

In operation of the hand power tool, the striking of the teeth betweenthe pinion gearing 121 and the spur gearing 131 is damped by the dampingelements 22, causing a marked reduction in the gear rattling that isclearly perceptible in conventional hand power tools, particularly uponstartup or shutdown of the hand power tool. The front damping elements22, in terms of the direction of rotation, are particularly decisive forthis; they damp the impacts that occur counter to the direction ofrotation.

In work with the hand power tool, it sometimes happens that the toolbriefly catches in the workpiece. In work with right angle grinders andcutting wheels, for instance, this often occurs. In this catching, whichis equivalent to a brief blockage of the tool, extreme forces areexerted on the gearings 121, 131 between the driving gear wheel 12 andthe driven gear wheel 13. These force peaks are effectively attenuatedby the damping elements 22, leading to a reduction in the recoil momentthat the user cannot fail to perceive, thus making tool use morecomfortable for the user. Overall, the mechanical loads on the gearmechanism are reduced, which leads to longer service lives andperceptibly greater comfort, since gear vibrations, impacts and the likeare transmitted to the tool housing only greatly attenuated.

In the exemplary embodiment shown in FIGS. 1 and 2, the pockets 21 areembodied with a rectangular inside cross section, which is defined inthe circumferential direction by two radial, flat side walls 211. Theradial ribs 18 that protrude into the pockets 21 have a rectangularcross section. The damping elements 22 may have an arbitrary geometry.In the exemplary embodiment, they are embodied for instance as elasticroller-like bodies, which are oriented parallel to the axis of thedriven shaft 14. It is understood that modified geometries of thepockets 21 and radial ribs 18 are possible, and the number of radialribs 18 and correspondingly the number of pockets 21 may also be varied.

FIG. 3 shows a matrix that illustrates possible combinations of pocketgeometries and radial rib geometries. Various internal profiles of thepockets 21 are plotted In the top line, while various profiles of theradial ribs 18 are plotted in the column on the left. All the pocketprofiles A, B, C and D may be combined with the corresponding radial ribprofiles in lines 1, 2, 3 and 4. The matrix is self-explanatory, and soonly a few of its special features will be pointed out here:

In column C, the pocket 21, as in the exemplary embodiment of FIGS. 1and 2, has flat side walls. In columns A, B and D, the side walls areprovided with convexities, which can be embodied either in curved orangular form. Upon the deformation of the damping elements 22, theseconvexities accommodate a portion of the material of the dampingelements 22, so that the spring properties of the damping elements 22are improved. As shown in the left-hand column, the profiles of theradial ribs 18 may be embodied as rectangular, wedge-shaped, andrectangular with concavities (line 3) and convexities (line 4). In allthe instances of combinations of the pocket profile and radial ribprofile, the damping elements 22 are braced, as before, on the radialrib 18 and on the two side walls 211 of the pockets 21. In thecombinations A/1, A/2, A/3, B/3, C/3, and D/3, the damping elements 22are embodied as either spherical or roller-shaped; in the case of theroller shape they extend in the radial direction.

1. A gear mechanism, in particular for hand power tools, having adriving gear wheel (12), seated in a manner fixed against relativerotation on a drive shaft (11), and a driven gear wheel (13), meshingwith the driving gear wheel and driving a driven shaft, characterized inthat spring- elastic damping elements (22) are located between thedriven gear wheel (13) and the driven shaft (14).
 2. The gear mechanismof claim 1, characterized in that the driven gear wheel (13) is seatedrotatably on the driven shaft (14) and has pockets (21), offset from oneanother in the circumferential direction, that are defined by radialside walls (211); and that the damping elements (22) rest in the pockets(22) with contact against the radial side walls (211) and are retainedon a slaving device (16) that is joined to the driven shaft (14) in amanner fixed against relative rotation.
 3. The gear mechanism of claim2, characterized in that the slaving device (16) is fixed axiallynondisplaceably on the driven shaft (14).
 4. The gear mechanism of claim3, characterized in that the driven gear wheel (13) is braced in theaxial direction on the one side on an annular shoulder (15) embodied onthe driven shaft (14) and on the other on the slaving device (16). 5.The gear mechanism of claim 2, characterized in that the slaving device(16) has a ring (17), seated on the driven shaft (14), and a number ofradial ribs (18) corresponding to the number of pockets (21) in thedriven gear wheel (13), of which ribs one protrudes into each pocket(21); and that two or more damping elements (22), resting on each sideof the radial rib (18), are provided in each pocket (21), of whichdamping elements each one is braced on the radial rib (18) and on aradial side wall (211) of the pocket (21).
 6. The gear mechanism ofclaim 5, characterized in that the ring (17) of the slaving device (16)is pressed onto the driven shaft (14).
 7. The gear mechanism of claim 5, characterized in that the ring (15) of the slaving device (16) isjoined in force-locking fashion to the driven shaft (14).
 8. The gearmechanism of claim 3, characterized in that the radial side walls (211)of the pockets (21) have indentations in the region of contact with thedamping elements (22).
 9. The gear mechanism of claim 3, characterizedin that the radial ribs (18) of the slaving device (16), at least intheir region protruding into the pockets (21), have a rectangularprofile, with or without concavities or convexities, or a wedge-shapedprofile.
 10. The gear mechanism of claim 1, characterized by itsembodiment as an angular gear, in which the driven gear wheel (13) isembodied as a ring gear with spur gearing (131), and the driving gearwheel (12) is embodied as a conical pinion with pinion gearing (121).